Ala. Code § 8-8-11: Application of Partial Payments to Principal and Interest.

Except as provided in this section, when partial payments are made, the interest due is first to be paid and the balance applied to the payment of the principal. In the case of a judgment for child or spousal support, or a judgment for medical support of a child or spouse, any partial payment shall be applied first to the principal, and the remaining balance, if any, shall be applied to the interest.